From the very first, the magnetic recording industry has constantly and dramatically increased the performance and capacity of hard disk drives to meet the computer industry's insatiable demand for more and better storage. Not so long ago, a 40 MB disk drive was a big deal. Today it's a door stop, and a 1 GB drive is a minimum for most desktop computers. Applications like multi-media, real-time video and audio, and graphical user interfaces, along with ever-increasing program sizes, are driving the need for ever-increasing storage capacity.
To meet these needs, the magnetic recording industry has been increasing the areal density storage capacity of hard drives at a historical rate of roughly 27 percent per year. In recent years, the growth rate itself has increased to as much as 60 percent per year with the result that today's disk drives store information in the 600 to 700 Mb per square inch range. By the year 2000 the areal density requirements are expected to reach 10 Gb per square inch. Sustaining this growth rate into the next century requires progressive advances in all technologies used to fabricate hard disk drives.
The read-write head technology that has sustained the hard disk drive industry to date is based on the inductive voltage produced when the a permanent magnet (i.e. the disc) moves past a wire-wrapped magnetic core (i.e., the head). Early recording heads were fabricated by wrapping wire around a laminated iron core analogous to the horseshoe-shaped electromagnets found in elementary school physics classes.
Market acceptance of hard drives, coupled with increasing areal density requirements, fueled a steady progression of inductive recording heading advances. This progression culminated in advanced thin-film inductive read-write heads that are fabricated using semiconductor-style processes in volumes large enough to meet the insatiable demands of the computer industry for data storage. Even though advances in inductive read-write head technology have been able to keep pace with increasing areal density requirements, the ability to cost-effectively manufacture these heads is nearing its natural limit, hence a new recording head technology, the magneto-resistive (MR) head is currently being implemented to fuel the disk drive industry's continued growth in capacity and performance.
The magneto-resistive head not only increases the areal density of a given disk drive but enables the more rapid retrieval of data therefrom. One of the reasons for this is that the MR head is flown at a substantially lower distance from the disk surface than previous inductive read-write heads. This "flying height" has been steadily decreasing as recording technology advances. Currently the flying height of most read-write heads is measured in millionths of an inch. The new magneto-resistive head technology enables flying height's measured in Angstroms. Given this extremely small separation between the read-write head and the disk surface, it will be appreciated that even the previously acceptable microscopic faults in disk surface texture now present a source for catastrophic failure.
Current manufacturing practice is to use a randomly super-polished substrate, and after polishing, the recording surfaces of each disc are individually textured with a near circumferential pattern over the previously super-polished area, bringing the area to a desired roughness, or texture. This texturing is performed as a single or double texture step on texture machine. One such machine is an EDC-1800 (Exclusive Design Co., Inc., San Jose, Calif.). This process presents several problems.
A first problem is that the scratches formed by the random polishing are not reliably and completely removed from the recording surface after the texture has been applied to the polished disk. Instead, the texture is superimposed on the random scratches, which results in a relatively uneven surface. This in turn forms a disk surface from which all recorded signals cannot be reliably retrieved for reliable playback. In the worst case, the unevenness formed by this methodology allows protrusions above the disk surface which will destroy a magneto-resistive head flying in close proximity thereto.
A second problem is that current polishing methodologies utilize a polishing pad which is used to produce disks in a batch process. In this batch-oriented methodology, a previously specified number of disks are sequentially polished using the same pad surface. This causes an uneven wear state of the polishing pad with a concomitant uneven distribution of the polishing material disposed on the polishing pad. This in turn leads inevitably to uneven roughness and scratch counts on the surface of the disk so formed, with all the previously discussed problems.
What is clearly needed is a methodology which provides for a smoother disk surface than the current super-polish/texture methodology. The key problem to this former methodology is clearly the unwanted interaction between the random super-polish scratches overlaid by near-circumferential texturing scratches. In other words, what is needed is methodology which either obviates or completely eliminates the random super-polish scratches.
What is further needed is a methodology which is inherently more uniform than the current batch process for polishing and texturing disks, leading to increased efficiency of manufacturing through reduced manufacturing and post-deployment failures.
It would be further desirable if the methodology could be implemented without completely re-engineering or replacing existing polishing and texturing equipment.